The way control of the CPU is transferred from one instruction to the next one.

Remember — The question is, “Who’s controlling the CPU?”

Control Flow Graph

TODO Control flow graph explanation

TODO Example of control flow graph with code parallel.

Professor’s Opinion: A function written by a good programmer only has one exit point.

• If it has multiple exit points, it breaks modular reasoning.

Unconditional Jumps

Transfers control from one instruction to another unconditionally.

...
goto LABEL_A
LABEL_A:
...

Issues — The ability to jump anywhere leads to the spaghettication of code.

• “Goto considered harmful”

Restricted Unconditional Jumps

Two-Way Selection Statements

Fancy way of saying if-then-else.

if B then S_1 else S_2 end

Design Issues:

• Type and Form: Can you do anything other than booleans?
• Nesting Semantics: Are nested conditionals allowed?

Multiple Selection Statements

You know what these are (TODO)

select option in:
  case v_1 do s_1
      ...
  case v_2 do s_2
      ...
  case v_3 do s_3
      ...
  default
      ...

Design Issues:

• Form and type of option expression: Does it have to be an enumerated type?
  • e.g., C only lets you do integers, which are technically enumerated types
• Specification of case values: Can we do non-exhaustive cases? Do you have to provide a default case?
• Restrictions on executing multiple cases: Can you execute multiple cases? Can you fall-through breaks (cascading semantics)?

Iterative Statements

Counter Controlled Loops

A way to introduce primitive recursion. Basically, any iteration that does a finite number of predetermined iterations.

for i \leftarrow init to n do S end

Design Issues:

• Type and scope of counter variable: Is it an int? Is the scope the body of the loop?
• Read-only: Is the counter variable read-only in the body?

Generalized Loops

Basically a pretty while loop. A more general version of the above.

for i \leftarrow init until B(i) with update(i) do S end

Logically-Controlled Loops

while B do S end